.\"	$OpenBSD: SSL_CTX_set_cipher_list.3,v 1.1 2016/11/05 15:32:19 schwarze Exp $
.\"	OpenSSL b97fdb57 Nov 11 09:33:09 2016 +0100
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.Dd $Mdocdate: November 5 2016 $
.Dt SSL_CTX_SET_CIPHER_LIST 3
.Os
.Sh NAME
.Nm SSL_CTX_set_cipher_list ,
.Nm SSL_set_cipher_list
.Nd choose list of available SSL_CIPHERs
.Sh SYNOPSIS
.In openssl/ssl.h
.Ft int
.Fn SSL_CTX_set_cipher_list "SSL_CTX *ctx" "const char *str"
.Ft int
.Fn SSL_set_cipher_list "SSL *ssl" "const char *str"
.Sh DESCRIPTION
.Fn SSL_CTX_set_cipher_list
sets the list of available ciphers for
.Fa ctx
using the control string
.Fa str .
The format of the string is described
in
.Xr openssl 1 .
The list of ciphers is inherited by all
.Fa ssl
objects created from
.Fa ctx .
.Pp
.Fn SSL_set_cipher_list
sets the list of ciphers only for
.Fa ssl .
.Pp
The control string
.Fa str
should be universally usable and not depend on details of the library
configuration (ciphers compiled in).
Thus no syntax checking takes place.
Items that are not recognized, because the corresponding ciphers are not
compiled in or because they are mistyped, are simply ignored.
Failure is only flagged if no ciphers could be collected at all.
.Pp
It should be noted that inclusion of a cipher to be used into the list is a
necessary condition.
On the client side, the inclusion into the list is also sufficient.
On the server side, additional restrictions apply.
All ciphers have additional requirements.
ADH ciphers don't need a certificate, but DH-parameters must have been set.
All other ciphers need a corresponding certificate and key.
.Pp
A RSA cipher can only be chosen when a RSA certificate is available.
RSA ciphers using DHE need a certificate and key and additional DH-parameters
(see
.Xr SSL_CTX_set_tmp_dh_callback 3 ) .
.Pp
A DSA cipher can only be chosen when a DSA certificate is available.
DSA ciphers always use DH key exchange and therefore need DH-parameters (see
.Xr SSL_CTX_set_tmp_dh_callback 3 ) .
.Pp
When these conditions are not met for any cipher in the list (for example, a
client only supports export RSA ciphers with an asymmetric key length of 512
bits and the server is not configured to use temporary RSA keys), the
.Dq no shared cipher
.Pq Dv SSL_R_NO_SHARED_CIPHER
error is generated and the handshake will fail.
.Sh RETURN VALUES
.Fn SSL_CTX_set_cipher_list
and
.Fn SSL_set_cipher_list
return 1 if any cipher could be selected and 0 on complete failure.
.Sh SEE ALSO
.Xr ssl 3 ,
.Xr SSL_CTX_set_tmp_dh_callback 3 ,
.Xr SSL_CTX_use_certificate 3 ,
.Xr SSL_get_ciphers 3
